Temperature-and field dependent characterization of a twisted stacked-tape cable

Abstract

The Twisted Stacked-Tape Cable (TSTC) is one of the major high temperature superconductor cable concepts combining scalability, ease of fabrication and high current density making it a possible candidate as conductor for large scale magnets. To simulate the boundary conditions of such a magnets as well as the temperature dependence of Twisted Stacked-Tape Cables a 1.16 m long sample consisting of 40, 4 mm wide SuperPower RE BCO tapes is characterized using the "FBI" (force -field -current) superconductor test facility of the Institute for Technical Physics (ITEP) of the Karlsruhe Institute of Technology (KIT). In a first step, the magnetic background field is cycled while measuring the current carrying capabilities to determine the impact of Lorentz forces on the TSTC sample performance. In the first field cycle, the critical current of the TSTC sample is tested up to 12 T. A significant Lorentz force of up to 65.6 kN m −1 at the maximal magnetic background field of 12 T result in a 11.8 % irreversible degradation of the current carrying capabilities. The degradation saturates (critical cable current of 5.46 kA at 4.2 K and 12 T background field) and does not increase in following field cycles. In a second step, the sample is characterized at different background fields (4 -12 T) and surface temperatures (4.2 -37.8 K) utilizing the variable temperature insert of the "FBI" test facility. In a third step, the performance along the length of the sample is determined at 77 K, self-field. A 15 % degradation is obtained for the central part of the sample which was within the high field region of the magnet during the in-field measurements.

Present Status and Recent Developments of the Twisted Stacked-Tape Cable Conductor

“…The results showed degradations of about 15% at 6 T and 10% at 12 T between the first measurement cycle and the second cycle. After the second cycle no further degradation was observed [11]. Nevertheless, the critical current values were much lower (~50%) than what was expected from single tape data.…”

“…A cycle test was performed between 6 T and 12 T. The critical currents measured at 5 µV/cm are shown in Fig. 2 [11]. The results showed degradations of about 15% at 6 T and 10% at 12 T between the first measurement cycle and the second cycle.…”

Design Optimization of Round Strands Made by Twisted Stacks of HTS Tapes

“…As a consequence, calculation of the critical current of the bent twisted strand must deal with both parallel and serial connections of superconducting elements. If the given strand's length l divided into N s elements and for each one the critical current of the cross section I c i is obtained according to (4), then the average critical current of the strand I c is a solution for N s serial-connected superconducting regions problem…”

“…Noncomplete transposition of the tapes in TSTC concept (inductance of the tape depends on its position in the stack) can lead to a nonuniform current distribution between tapes in ac or transient operating regimes. First high-field-low-temperature tests of the TSTC conductor showed a necessity of additional mechanical reinforcement against the acting Lorentz force [4].…”

Cryomak – The Overview of Cryogenic Testing Facilities in Karlsruhe

“…The main parameters are the following: Imax = 10 kA; Bmax = 12 T; Fmax= 100 kN. Especially high temperature superconducting cables are of interest with respect to power and magnet applications [17,18].…”